To solve numerous problems including inconvenience in an operation of using an end plate in a stacker bundler, inconvenience in an operation of cutting a protective sheet from a roll of paper, an irregular position of the protective sheet, or the like.

A protective sheet feeder comprises a pusher for moving an assembly W of signatures to a bundling section, a protective sheet storage device H for supporting the protective sheet, a protective sheet take-out means K for taking out the protective sheet from the protective sheet storage device, a protective sheet sender comprising a protective sheet holding means L for receiving and releasing the protective sheet and a protective sheet moving means M for moving the protective sheet to a position corresponding to the protective sheet holding means, a pair of protective sheet receiving guide frames 72 and 72A provided to be capable of receiving ends of the protective sheet released from the holding means from a lower surface of a moving space of the assembly to a lower position, and a protective sheet folder N for moving the protective sheet supplied to the guide frames synchronously with the movement of the assembly from between the pair of guide frames to the bundling section for folding a lower part of the protective sheet onto a lower surface of the assembly.